Centrifugal wafer carrier cleaning apparatus

ABSTRACT

Apparatus (20) for cleaning carriers used to hold semiconductor wafers, substrates, data disks, flat panel displays and similar containers used in applications highly sensitive to contamination. The apparatus has a processing bowl (21) with entrance and exit ports (34, 36) through which carriers are installed and removed from processing chamber (21). Rotor (70) rotates within the processing chamber. Rotor (70) includes a rotor cage (71) which mounts detachable wafer carrier supports (214). Filtered, heated air is passed through the process chamber for drying. Cleaning liquid and additional drying gas can be supplied through manifolds (120, 110) positioned inside and outside rotor cage (71).

This is a continuation of U.S. patent application Ser. No. 07/901,614,filed Jun. 15, 1992, now U.S. Pat. No. 5,224,503.

TECHNICAL FIELD

The technical field of this invention is cleaning apparatus for rinsingand drying carriers used to hold and process semiconductor wafers,substrates, flat panel displays and similar articles requiring extremelylow contamination levels.

BACKGROUND ART

The processing of semiconductor wafers and substrates is very sensitiveto problems of contamination. This is also true with photomasks, flatpanel displays, data disks, and other articles relating to thesemiconductor industry. These articles require extremely lowcontamination levels. Even minute contaminants can cause defects tooccur in the processing of these low-contamination wafer articles.Accordingly, it is necessary to maintain a high level of cleanlinessduring all or nearly all stages of production.

Semiconductor wafers, substrates, .photomasks, flat panel displays andother similar low-contamination wafer products are also typicallyprocessed in batches. Batch handling may occur throughout the entireproduction process, or for one or more processing steps or relatedhandling operations. Batch processing of this type almost alwaysutilizes some type of carrier or carriers to hold the thin wafer-likematerials being processed.

In the batch processing of semiconductor substrates and wafers, a wafercarrier is used to hold a group of these articles. The wafer carrierscan be of various designs and are more specifically referred to as awafer boat. In many applications the wafer boat is made of a suitablepolymeric material, e.g. polypropylene or TEFLON® fluoropolymer. Thesides and sometimes the bottom of the wafer boat have receiving slotsformed to receive and positionally restrain the wafers in a spaced arraywith the faces of the wafers adjacent one another. Typically, thecentral axes of the wafers are aligned. The wafers are slid into theboat, such as from the side or above and removed by sliding themoutwardly. The receiving slots in the wafer boat are shallow so that thewafer is engaged only at the peripheral edges and along a thin marginalband extending inwardly from the periphery.

Wafer carriers can also be provided in the form of a protective case orbox in which the wafers are held and enclosed against contaminationduring travel within the processing facility. Wafer carriers of thistype are frequently designed to hold a wafer boat having a complementarydesign. The complementary relationship of the protective wafer carrierbox and the wafer carrier boat allow the boat and supported wafers to befully enclosed and positionally restrained in all directions duringtransport.

The manufacture of wafer carriers also includes their cleaning. Cleaningof wafer carrying boxes and wafer carrying boats is difficult becausethey typically have features which include slots, grooves or apertureswhich are difficult to fully clean. This is greatly exacerbated by theextremely low contamination levels which can be accepted for articlesused directly or indirectly in processing of the wafer articles. Dust,metal particles, oils and other organic chemicals may be present on thesurfaces of the molds or other production tools used to make wafercarriers. Fully cleaning the wafer carriers to the required extremelylow contamination levels is also difficult. Cleaning the wafer carriersfor use in semiconductor processing is a task which in some cases isalmost as difficult as mechanically forming the article.

The cleaning of wafer carriers has until this invention remained adifficult and relatively costly procedure. The current invention hasseveral advantages and benefits which are explained or otherwiseindicated herein.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more preferred forms of the invention are described herein withreference to the accompanying drawings. The drawings are brieflydescribed below.

FIG. 1 is a front elevational view of a preferred embodiment of cleaningapparatus according to the current invention.

FIG. 2 is a rear elevation view of the apparatus shown in FIG. 1.

FIG. 3 is a left side elevational view of the apparatus shown in FIG. 1.

FIG. 4 is a right side elevational view of the apparatus shown in FIG.1.

FIG. 5 is a top view of the apparatus shown in FIG. 1.

FIG. 6 is a rear elevational view of the apparatus shown in FIG. 1 withportions removed for purposes of illustration.

FIG. 7 is an additional rear elevational view of the apparatus shown inFIG. 1 with further portions removed for purposes of illustration.

FIG. 8 is a longitudinal sectional view of selected portions of theapparatus of FIG. 1 showing the rotor and drive construction.

FIG. 8A is a longitudinal sectional view showing a portion of FIG. 8 ingreater detail.

FIG. 8B is a longitudinal sectional view showing a portion of FIG. 8 ingreater detail.

FIG. 9 is a cross sectional view taken along line 9--9 of FIG. 7.

FIG. 10 is a top view of the rotor shown in isolation.

FIG. 11 is a side view illustrating a preferred wafer carrier supportconstruction used in the apparatus of FIG. 1 shown in isolation with therotor assembly.

FIG. 12 is a detail top view showing in isolation a preferred doorconstruction used in the apparatus of FIG. 1.

FIG. 13 is a detail front view showing in isolation the preferred doorconstruction of FIG. 12.

BEST MODES FOR CARRYING OUT THE INVENTION AND DISCLOSURE OF INVENTION

FIG. 1 shows a preferred centrifugal wafer carrier cleaning apparatus 20according to this invention. Apparatus 20 includes a processing bowl orvessel 21 and a frame 22. Frame 22 has a number of frame members 23which run both vertically and horizontally and are joined together toform an assembly which acts as the structural framework of apparatus 20.External finish panels 24 are detachably mounted between the framemembers using suitable fasteners. As shown the finish panels are adaptedfor convenient detachment and reinstallation using a panel mountingsystem. The panel mounting system advantageously includes panel latchassemblies which utilize latch activators 25 to controllably latch andunlatch the finish panels. The latch activators 25 are connectedmechanically to latch pins (not shown) which engage with the framemembers 23 at suitable locations. The finish panels can be temporarilyremoved to allow maintenance upon internal components. The assembly offrame 22 and finish panels 24 in combination form the exterior or outersurfaces of cleaning apparatus 20.

Wafer carrier cleaning apparatus 20 includes a front side 26, rear side27, right side 28, left side 29, top side 30, and bottom side 31. Frontside 26 has an associated entrance closure or first door 33 which iscontrollable to open and close a first opening Or entrance port 34formed in the sidewall of processing vessel or bowl 21. Rear side 27 hasan associated exit closure or second door 35 which is controllable toopen and close a second opening or exit port 35 which is also formed inthe sidewall of processing bowl 21. FIGS. 1 and 2 show doors 33 and 35in fully closed positions wherein the entrance and exit ports 34 and 36are closed and substantially sealed shut to prevent fluid leakage.

FIG. 11 shows that doors 33 and 35 are preferably supported upon a doorsupport structure having upper and lower guides 38 and 39. Guides 38 and39 are advantageously connected to inner and outer vertical connectionbars 41 and 40. The inner connection bar 41 has journal extensions 43which are supported in bearing blocks 44 (see FIG. 6) mounted upon frame22. The door support structures for doors 33 and 35 are mounted behindthe adjacent central finishing panels 24a and 24b. The corners of doors33 and 35 are provided with rollers 42 which roll upon the guides 38 and39. Doors 33 and 35 are preferably operated relative to the door supportstructures by pneumatic rams 37. The door support structures and doorsare pivoted inwardly to seal against the peripheral flange of theentrance and exit ports. This is done by controllably pivoting the doorsupport structures using a door pivot actuator 45 which isadvantageously a pneumatic ram extending between the outer vertical bar40 and an adjacent frame member 23 (shown in phantom in FIG. 12).

The door is operated in the following manner. The pivot actuator 45 ismaintained in an extended position until the door 33 has been fullyextended toward the outer vertical bar 40. The pivot actuator is thenoperated to retract the door and support assembly formed by the door anddoor support structure. Conversely, when opening the door the pivotactuator is first extended to move the door and support assemblyoutwardly from the processing bowl 21. Thereafter the door is rolledupon the guides 38 and 39 and retracted toward the inner vertical bar41.

The bottom 31 of apparatus 20 is advantageously provided with a set ofcasters 48 which are connected to the frame 22 near the bottom corners.The bottom corners of apparatus 20 are also preferably fitted withextendible and retractable stabilizers 49. The stabilizers have a fixedupper part 49a which is connected to the frame. A lower extendible part49b is adjusted relative to the upper part. Apparatus 20 can thus berolled to a suitable location. Thereafter the stabilizers can beextended to transfer the weight of the apparatus from casters 48 to thestabilizers and provide increased stability.

FIG. 1 shows that the wafer carrier cleaning apparatus 20 includes threesections 51-53; herein termed the upper of first section 51, the middleor second section 52, and the lower or third section 53. The upper orfirst section 51 includes a primary drying gas treatment system. Theprimary drying gas treatment system includes a suitable primary dryinggas filter 55 shown in FIG. 2. Filter 55 is received within the outerportions of the drying gas plenum 57. FIG. 6 shows that the preferredconstruction of the plenum includes a filter stop 67 which extends aboutthe interior of the plenum adjacent to but spaced inwardly from thefilter opening 58. The filter 55 is installed within the plenum and isin part retained by the filter stop 67. Two connection brackets 68 areadvantageously included at the sides of filter opening 58 to assist inmounting a finishing panel which also serves to support the outer faceof the filter and keep the filter in the installed position.

In a typical installation the exit or rear side 27 of the apparatus iswithin a clean room or similar low contamination environment. Air can bepulled from the clean room and through the filter 55. Filter 55 ispreferably a HEPA type or other suitable filter capable of removing verysmall particulate matter with great effectiveness. Filter 55 isconstructed with a relatively large surface area to minimize pressuredrop associated with moving air or other drying gas therethrough. Thisis helpful in eliminating the need for a specific, dedicated drying airfan which would otherwise increase particulate contamination.Contamination could occur to the primary drying gas flow path if aspecific, dedicated drying gas fan was included therein. Such ahypothetical construction could also lead to contamination to theinterior processing chamber 47 of vessel 21. Primary drying gas passesthrough the processing chamber to remove moisture therefrom. Ahypothetical fan and associated drive motor which is specificallyfunctions to move primary drying air or other drying gas also generatessignificant amounts of general contamination within or adjacent to thewafer carrier cleaning apparatus. This general contamination outside theprocessing vessel 21 nonetheless causes particulate matter to enter theprocessing chamber and prevents the very low contamination levels neededin the processing of semiconductor and other low-contamination waferproducts.

FIG. 6 shows that the upper section 51 of the wafer carrier cleaningapparatus also preferably includes a drying gas heater 56. Drying gasheater 56 is mounted within a primary drying gas plenum 57. Plenum 57serves as a drying gas enclosure and conduit. Air or other drying gas ispassed through filter 55. Filter 55 is mounted within a plenum intakeopening 58 which is substantially the entire side of the plenum.Filtered air received within the plenum passes about heater 56. Airwithin the plenum also passes down through a central heater opening 61which extends through the lower section 62 of the heater. Heater 56 alsohas an upper section 59 which is provided with a cover that encloseswiring connections and mounts for an array of spaced parallel electricalresistance heating elements 60 mounted within the lower section of theheater and across the central opening 61. Each heating element 60 ispreferably provided with a multitude of fins to improve heat transfer tothe air or other primary drying gas passed thereover.

Air passes down through the central heater opening 61 and from theplenum through a plenum exhaust opening 63 in the central bottom of theplenum. The plenum exhaust opening is open to a processing bowl top port65 (FIG. 7). Opening 63 and top port 65 allow communication of filtered,heated drying gas from the plenum into the processing vessel at aposition substantially aligned with the central axis of the processingchamber and the rotational and longitudinal axis of rotor 70.

The primary drying gas plenum 57 is also preferably provided with astatic electricity suppressor 66. Static suppressor 66 can be selectedfrom suitable types of commercially known units. It preferably hasexposed electrodes which are charged to desired electrical potentials tohelp neutralize static electricity generated by movement of drying gasthrough plenum 57 and over associated surfaces of the plenum andenclosed heater 56. The particular operating parameters used may varydependent upon environmental and climatic conditions.

FIG. 6 shows that the middle or second section 52 includes theprocessing vessel or bowl 21. The processing bowl 21 is mounted upon theframe 22 using suitable fasteners (not shown). Processing bowl 21 isroughly cylindrical having semicircular sidewall sections 72. Thesidewall of the processing bowl is completed by two substantially flatpanels 73 on the opposing front and rear sides. The first or entranceflat sidewall panel includes the first or entrance port 34. The exit orsecond flat sidewall panel includes the second or exit port 36. Both theentrance and exit ports are preferably built with port flanges 74 whichare relatively thicker than the sidewall panels 73 to strengthen thevessel and provide surfaces against which the doors 33 and 35 can seal.FIG. 6 has been simplified by not showing the rotor assembly 70 throughthe port 74. The details of the rotor and other internals of theprocessing bowl are described in connection with FIG. 7

FIG. 7 shows that the processing bowl also has a top wall 76. The topwall is most preferably a relatively low flat frustoconical shape. Thetop wall has the top port 65 which serves as a primary drying gas supplyformed therethrough. Port 65 thus provides an inlet to primary dryinggas flowing from the plenum 57 into the processing chamber 47.

The processing bowl also has a bottom wall which is of compositeconstruction. FIG. 8 illustrates specifics of the preferredconstruction. The first part of the bottom wall is an outer bottom wallpiece 77 which is annular and connects to the lower edges of theprocessing bowl sidewall sections 72 and 73. The central portion of thebottom wall is open to provide a construction which accommodatesinherent vibration of the rotating assembly and associated drive whichwill be described in greater detail hereinafter. This constructionutilizes a flexible membrane or diaphragm 78 which is annular andextends inwardly from the inner edge of an annular outer bottom wallpiece 77. The outer edge of the annular diaphragm 78 is captured betweenthe outer bottom wall piece 77 and an outer diaphragm retaining ring 79which is connected thereto using suitable fasteners. The inner edge ofdiaphragm 78 is raised relative to the outer edge, and is connected to adrive mount base plate 80. A diaphragm inner edge retaining ring 81 isconnected by fasteners below the base plate 80 to capture diaphragm 78therebetween.

The processing chamber 47 is also most preferably provided with a falsebottom or bottom baffle 85. The bottom baffle is sized to provide aspace between its outer periphery and the inside surfaces of theprocessing bowl sidewalls. This annular exhaust and drain baffle spaceallows exhausting gas and draining liquids to flow across and down aboutthe outside of the baffle. Bottom baffle 85 is most preferablyconstructed using two baffle parts, an upper or first baffle part 86,and a lower or second baffle part 87. The upper baffle part is flat, ormore preferably, slightly crowned to drain liquids which fall thereon.The lower baffle part 87 is frustoconical expanding upwardly to connectwith and support the peripheral edge of the upper baffle part 86. Thebottom baffle assembly 85 is supported upon baffle mounting brackets 88which extend upwardly from the outer bottom wall 77 to connect with thelower baffle part 87.

The processing vessel 21 is preferably fitted with at least one outerspray manifold 90. Outer spray manifolds 90 are connected directly tothe sidewalls 72. External spray manifold supply fittings 91 connectwith liquid supply conduits 92. As shown, processing chamber isadvantageously provided with four (4) outer spray manifolds 90 at spacedapproximately equiangular points about the central axis of theprocessing chamber. The outer spray manifolds are provided with aplurality of liquid spray nozzles 93. Spray nozzles 93 are directedinwardly to spray water, water and detergent, solvents, mixturesthereof, or other cleaning liquids generally inward or directly towardthe central axis of the processing chamber.

FIG. 7 shows that the processing vessel 21 is also preferably fittedwith at least one outer drying gas manifold 100. Outer drying gasmanifolds 100 are similar to outer cleaning liquid spray manifolds 90 inbasic construction and mounting to the processing vessel sidewall 72.The outer drying gas manifolds are supplied with a suitable pressurizedsecondary drying gas through supply fittings 101 mounted in the sidewall72. The supply fittings 101 (see FIG. 6) are connected to secondarydrying gas supply conduits 102. These conduits are supplied with asuitable secondary drying gas, such as clean dry air or nitrogen. Thedrying gas manifolds have gas nozzles or jets 103. Jets 103 are inwardlydirected to provide streams of secondary drying gas which impinge uponthe wafer carriers being dried. As shown, there are four (4) outersecondary drying gas manifolds 100 which are spaced approximatelyequiangularly about the processing chamber. The gas manifolds and spraymanifolds are advantageously arranged in alternating sequence about thediameter of the circular outer manifold array formed by manifolds 90 and100.

FIGS. 7 and 9 also indicate that processing chamber 47 is preferablyprovided with a number of inner liquid spray manifolds 110 and innersecondary drying gas manifolds 120. The function of manifolds 110 is tospray cleaning and rinsing liquid(s) at wafer carriers mounted upon therotor 70. The inner spray manifolds are mounted in a circular array atapproximately equiangularly spaced positions, as shown in FIG. 9. Theinner liquid spray manifolds are mounted to the bottom baffle 85 andextend upwardly at radial positions which are within the cage 71 ofrotor 70. The wafer carriers being cleaned and dried are mounted uponthe rotor cage 71, in a suitable manner, such as indicated below. Theinner liquid spray manifolds 110 are provided with a plurality ofnozzles 113 mounted upon the manifolds at spaced vertical locations. Thenozzles are directed in a generally outward or radial direction towardthe rotor cage.

FIG. 9 shows an array of inner secondary drying gas manifolds 120interpositioned in an alternating pattern with the inner liquid spraymanifolds 110. As shown there are four (4) manifolds 120 which areapproximately equiangularly arranged about the central axis of theprocessing chamber and the rotational axis of rotor 70. Manifolds 120have a plurality of vertically spaced nozzles or jets 123 arranged alongthe upstanding manifolds. The jets direct diverging streams of secondarydrying gas in a generally outward direction toward the rotor cage 71 andagainst wafer carriers supported thereon. The drying gas is used to blowand evaporate any rinsing or washing liquids from the surfaces of therotor and supported wafer carriers being cleaned.

Liquid supplied to spray manifolds 90 and 110 and secondary drying gassupplied to manifolds 100 and 120 are preferably controlled by anautomatic controller (not shown) which operates electrical solenoidvalves (not shown). The electrical solenoid valves control the flow ofcompressed air or other pneumatic control gas or other suitable fluid.The control gas is controllably delivered to pneumatically controlledsolenoid valves which directly control the flow of cleaning liquids anddrying gas to the manifolds 90 and 100. Manual cleaning fluid supplyvalves (not shown) and manual secondary drying gas valves (not shown)are also connected in parallel with the pneumatically controlled valvesto allow manual operation if desired.

Pressure gauges 95 (see FIG. 4) are advantageously used to provide anindication of the pressures to the spray and gas manifolds. Associatedpressure regulator valves 96 are also included to allow manualregulation of the delivery pressures to the manifolds.

The processing vessel 21 is also provided with a suitable means fordraining liquids therefrom. It is further provided with a suitable meansfor exhausting the drying gases. As shown, wafer carrier cleaningapparatus 20 includes a liquid drain and gas exhaust subsystem 130 whichin part combines these functions. The drain and exhaust subsystem 130includes an outflow box 131. Outflow box 131 is mounted beneath thebottom wall of the processing bowl 57. The outer bottom wall piece 77has a processing chamber outflow opening or port formed therethroughadjacent to the outflow box. Liquids drain across the bottom wall of theprocessing bowl and into the outflow box. Gases flow from the processingchamber through the outflow port and into the outflow box 131. Thebottom of the outflow box is sloped toward a central trough and a liquidoutflow drain opening 134. A liquid drain line or conduit 133 extendsfrom the drain opening 134 and carries liquids draining from theprocessing chamber to a suitable facilities drain pipe or sewer.

The outflow box 131 also has a gas exhaust port 135 which passesexhausting gases from the outflow box into a suitable gas exhaustconduit. As shown, the gas exhaust conduit is in the form of anupstanding exhaust gas stack 136. Exhaust stack 136 is connected to asuitable facilities exhaust system to remove the gas and containedliquid vapors removed from the processing chamber.

FIG. 7 shows portions of a rotating assembly which includes the rotor 70with attached rotor cage 71. The rotor is supported in an uprightposition by a rotor housing 140. Rotor housing 140 is mounted upon baseplate 80. Base plate 80 is supported upon frame drive assembly mountingmembers 23a which extend in a generally front-to-back orientation.Members 23a are a weldment subframe which attaches to the frame 22. Thisis advantageously accomplished using a drive assembly mounting ring 82which is bolted to members 23a. Elastic mounting bushings 83 areinterpositioned between the base plate and mounting ring 82 toaccommodate vibration and shock. Fasteners 84 extend through aperturesin fastener caps 89, ring 82, bushings 83 and base plate 80, to securethe base plate to the frame in a manner suitable for dissipatingvibration and shock.

A drive motor 150 is mounted beneath the base plate 80 to drive therotating assembly. Motor 150 extends downwardly into the lower or-thirdsection 53 of the wafer carrier cleaning apparatus. Motor 150 ispreferably a brushless direct current type electrical motor to preventparticulate contamination associated with contacting electrical brushtype motors. The motor is positioned by complementary tapered alignmentrings 190.

FIGS. 8, 8a and 8b show in sectional view the rotor, rotor housing, anddrive components in greater detail. Rotor 70 includes a rotor shaft 144.Rotor shaft 144 is mounted for rotation within the rotor housing 140.The rotor housing includes an upper or first housing piece 141 and alower or second housing piece 142. The first and second housing piecesare connected by a series of fasteners 143. The rotor housing 140 isconnected to the base plate 80 using fasteners 145. The lower secondrotor housing also functions as a housing which encloses a brakeassembly 155.

FIGS. 8 and 8A show that rotor 70 is mounted for rotation within theupper rotor housing 141 using an upper or first bearing 147 and a loweror second bearing 148. The upper bearing is advantageously a double ballbearing with the outer race of the bearing positioned within an upperrotor bearing mounting sleeve 157. The mounting sleeve 157 is held byfasteners 160 to the upper, distal end of rotor support housing piece141. Mounting sleeve 157 also holds bearing seals 161 and 162 which sealthe bearing area to retain lubricant and prevent migration ofparticulates generated by the bearings. The first upper rotor bearingseal 161 is captured in position between the outer race of bearing 147and a retainer ring 165 held by fasteners 160. A shield 166 is alsoadvantageously included to protect seal 161. The second upper rotorbearing seal 162 is held in position using two spring retainer rings 163on both sides thereof. A suitable shield 164 is also advantageouslyused.

FIG. 8A also shows that the upper distal end of rotor shaft 144 ispreferably provided with a flange 168 having mounting apertures whichreceive bolts 169. A splash shield or cap 170 is held between the rotorwheel 171 and flange 168 using bolts 169. The shield cap 170 and rotorwheel 171 rotate with shaft 144.

FIGS. 8 and 8B show the lower rotor bearing mounting arrangement andadjacent components. Lower bearing 148 is of a type suitable to supportmost of the thrust loading caused by the weight of the rotatingassembly. Spherical contact self-aligning ball bearings are suitable.The inner rotating race of bearing 148 is held in position upon shaft144 using spring ring retainers 173. A bearing shield 174 is held inposition above bearing 148. The outer race of bearing 148 is held withina lower rotor bearing mounting sleeve 176. Mounting sleeve 176 isconnected to the lower or proximate end of rotor housing piece 141 usingfasteners 177. Mounting sleeve 176 also mounts a shaft seal 178 using aspring retainer ring 179.

The drive assembly also preferably includes a rotating assembly brake155. The brake assembly 155 is enclosed within the lower or second rotorhousing piece 142. The brake includes a rotating cylindrical brake part181 which is secured to the rotor shaft 144 and motor output shaft 151using a key 182 and two opposing spring retainer rings 187. The outerperiphery of the rotating cylindrical brake part 181 is contacted by aseries of brake contact pads 183. The brake contact pads 183 line theinterior face of a cylindrical annulus which serves as a brake actuator184. Brake actuator 184 is elastically deformable and is inflated bysupplying pressurized fluid to the internal expansion chamber 185. Wheninflated the contact pads are moved inwardly to rub against the outerface of the rotating brake part or drum 181. The rotating assembly canbe controllably stopped using the brake system 155. This is important inslowing the rotating assembly and in stopping the rotating assembly in asuitable position for loading and unloading wafer carriers. The rotatingassembly is freed to rotate by relieving the pressure within chamber185.

The rotating assembly also includes a rotor wheel 171 which is mountedto the upper distal end of the upstanding rotor shaft 144. Rotor wheel171 has a peripheral ring 192 which is connected to a hub 194 using aplurality of spokes 193. The spaces between the spokes are open tofacilitate a downward flow of primary drying gas from the primary dryinggas inlet port 65 into the space within the interior of rotor cage 71.

The rotor wheel supports the rotor cage 71. The rotor cage includes anumber of peripheral rings 196. The uppermost peripheral cage ring isadvantageously formed by peripheral ring 192 of rotor wheel 171. Thecage also includes a number of longitudinal connection bars 197 whichextend between the cage rings 196. Reinforcement pieces 198 connectbetween the rotor wheel and cage to add strength and they also provideaddition blade area for moving drying gas as the rotor turns.

The rotary motion of the rotor wheel and rotor cage cause centrifugalaction of the drying gas and thereby induces a flow of gas. The flow ofdrying gas is generally downward into the interior of the rotor cage,and then outward toward the peripheral sidewalls of the processingvessel. The bottom baffle 85 is spaced inwardly from the processingvessel sidewalls leaving an annular flow space thereabout. Thecentrifugal action of the rotor thus induces an outward flow whichproceeds outwardly and downwardly to form a downwash which exits throughthe annular opening about the bottom baffle. Beneath the bottom bafflethe gas flow proceeds across the bottom wall of the processing vesseltoward the drain and exhaust box 131. This construction maintains arelatively controlled drying gas flow path which carries liquid vaporsfrom the processing chamber and minimizes turbulence and complex gasflows near the bottom of the chamber which otherwise will occur andderogate the particle counts exhibited by the wafer carriers processedthrough the cleaning apparatus 20.

FIGS. 9-11 show a preferred construction providing wafer carriersupports 200 which hold wafer carriers in position for cleaning withinapparatus 20. As shown there are four (4) wafer carrier supports 200 atspaced, approximately equiangular positions about rotor cage 71. Thewafer carrier supports include an upper or first mounting bracket 201and a lower or second mounting bracket 202. The mounting brackets aresecured to the rotor cage rings 196 using suitable fasteners 203. Theupper wafer carrier mounting brackets include a main bracket piece 205.Connected thereto are an outer retaining lug 206 and an inner stop piece207, both of which are advantageously made of nylon or other suitablepolymer material. The lower mounting brackets 203 include a main bracketpiece 210 which mounts an outer roll bar 211 and an inner rest piece212.

The wafer carrier supports further include a detachable wafer carriersupport basket 214. Wafer carrier support baskets 214 have a perimetricframe 215 and a reticulated basket 216. The baskets have an openingdefined by the perimetric frame with the basket extending outwardly toform a wafer carrier storage space therewithin. The wafer carriers areheld along the inwardly directed side of the basket 216.

The wafer carrier supports are provided with bracket engaging ends 217and 218. The first or upper bracket engagement end 217 is adapted toengage with the upper or first mounting bracket 201. The second or lowerbracket engagement end 218 is adapted to engage with the lower or secondmounting bracket 202. First bracket engagement end 217 has a first endengagement loop 219 which extends approximately perpendicular to theplane defined by the perimetric frame 215. Loop 219 is directed from thebasket opening, or upwardly when the basket is laid flat and inwardlywhen installed upon the rotor. Loop 219 is lifted up and over outerretainer lug 206 and then lowered into the position shown at the left inFIG. 11. A retaining groove 220 is formed in the inward face of lug 206in order to receive and retain the loop in position. Centrifugal actionforces the loop into groove 220.

The second or lower bracket engagement end 218 has a loop 222 whichextends is curved to form three different sections. The first section223 is perpendicular to the plane of the basket opening. This firstsection extends in a direction along the end of the basket and oppositeto the direction of the first loop 219. The second section 224 of loop222 extends parallel to the plane of the basket opening and away fromthe basket. The first and second seconds are joined in a curve whichbears upon a curved outer-upper corner of the lower bracket rest orsupport piece 212. Loop 222 also has a third section which is extendsand is oriented similar to the first section 223. The second and thirdsections are joined by a curve which bears upon and rolls over the outerroll bar 211 as the basket is installed. The basket pictured at theright in FIG. 11 shows the starting position. The basket is then pivotedor rolled upwardly and lifted to allow the loop 219 to clear over thelug 206. The basket is then lowered or dropped into the installedposition shown at the left in FIG. 11.

The wafer carrier cleaning apparatus is used to perform a wafer carriercleaning process. The wafer carrier cleaning process begins by loadingthe wafer carriers into baskets 216. The entrance door 33 is then openedand the loaded baskets are installed upon the rotor through the entranceport 34. This is repeated until all wafer carrier supports have beenloaded, preferably with loads having about the same weight. Theoperation then involves closing the entrance door using the actuatingram 38. The closing also involves sealing and the entrance door to theentrance port 34.

Thereafter the wafer carriers are subjected to a cleaning process whichincludes rotating the rotor and spraying the wafer carriers with water,solvent, detergent or other washing and cleaning liquid(s) suppliedthrough the inner and outer liquid spray manifolds 110 and 90. Thecleaning using liquid spraying and rotating steps is performed forsufficient time to adequately cleanse all surfaces of the wafer carriersbeing cleaned. The simultaneous spraying and rotating serves to directthe sprays of liquid from differing directions to enhance solubilizationof dirt, grease and other contaminants which may be present upon thewafer carriers prior to cleaning.

After treating the wafer carriers with the cleaning liquids, a dryingprocess is advantageously performed. The drying process includessupplying the drying gases to the processing chamber. The primary dryinggas is supplied through plenum 57. This primary drying gas is treated byfiltering the incoming air or other primary drying gas. Then the primarydrying gas is treated by heating it to a desired temperature, such as inthe range of 100° F. to 300° F., or higher dependent upon the materialsfrom which the wafer carriers are constructed. The primary drying gas isalso treated by dissipating static electricity using the staticsuppressor 66. The filter, heated, and static electricity dissipatedprimary drying gas is then used by supplying it to the processingchamber 47. The flow of primary drying gas is developed by inducing theflow by rotating the rotor. The centrifugal action of the rotor thussucks primary drying gas through the filter, plenum and heater and intoand through the processing chamber. The induced flow of primary dryinggas performs a drying function upon the wafer carriers being rotatedwithin the processing chamber.

The wafer carriers are also preferably subjected to drying by supplyingpressurized secondary drying gas to the outer and inner drying gasmanifolds 100 and 120. The drying operation is enhanced by streaming orjetting the drying gases toward the wafer carriers while rotating thewafer carriers loaded upon the rotor. This simultaneous rotating andjetting with drying gas helps to expose the interstices of the wafercarriers to the drying action of the secondary drying gas as well as theprimary drying gas. The secondary drying gas can be clean dry air,nitrogen or other suitable drying gas supplies having low contaminationand low vapor content thus enhancing the rate of drying a speeding theoverall processing rate. The wafer carriers are subjected to bothprimary and secondary drying for sufficient time to effectuate a drycondition on all surfaces of the wafer carriers.

The wafer carriers are further processed by stopping the rotor andincrementally positioning the wafer carrier supports 200 adjacent to theexit port 36. After the first wafer carrier support is positionedadjacent to exit port 36, the process includes opening exit door 35using door operator 37. The wafer carrier support is then removed fromthe rotor by lifting the upper loop 219 clear of lug 206 and pivotingthe wafer carrier support downwardly into the loading position shown inFIG. 11 at the right. The wafer carriers can then either be removed fromthe basket or the entire wafer carrier support can be removed andunloaded elsewhere as deemed best.

It is further noteworthy that the wafer carriers are loaded from arelatively less clean room, sometimes called a "grey room". The cleansedunits are unloaded into a clean room having very low propensity forcontaminating the cleaned wafer carriers. Thus the wafer carriercleaning apparatus is preferably installed so that the entrance dooroperates in the grey room environment and the exit door operates in theclean room environment.

The wafer carrier cleaning apparatus is constructed using known welding,machining and other forming operations to provide the components andassemblies described in detail hereinabove. The processing chamber bowland other conduits which supply gas or liquids are preferably made ofstainless steel. Structural components can be made of steel or othersuitable materials.

Industrial Applicability

The invention is useful for cleaning wafer carriers, boxes for holdingwafer carriers, and analogous articles requiring very low contaminantlevels.

We claim:
 1. A centrifugal cleaner for cleaning carriers used insemiconductor processing, comprising:a frame; a processing vesseldefining a process chamber therewithin; at least one port to allowpassage of carriers relative to the process chamber; said port beingformed in a sidewall of the processing vessel; at least one door forcontrollably opening and closing said port; a rotor mounted for rotationwithin the process chamber; at least one carrier support which isaccessible through said at least one port; said at least one carriersupport being connected to said rotor for holding carriers duringcentrifugal cleaning; rotor drive means for controllably rotating saidrotor; a plurality of outer supplies for directing fluid against the atleast one carrier support from positions outward of the carrier support;a plurality of inner supplies for directing fluid against the at leastone carrier support from positions inward of the carrier support; atleast one drying gas supply for supplying drying gas to the processchamber to dry said cleaning liquid from carriers.
 2. A centrifugalcleaner for carriers according to claim 1 and wherein the rotor extendsupwardly from lower portions of the processing chamber.
 3. A centrifugalcleaner for carriers according to claim 1 and wherein the rotor extendsupwardly from lower portions of the processing chamber within a rotorsupport housing mounted within the processing chamber.
 4. A centrifugalcleaner for carriers according to claim 1 and wherein said plurality ofouter and inner supplies includes includes at least one outer sprayerfor spraying from an outer position inwardly toward carriers held in thecarrier supports, and at least one inner sprayer for spraying from aninner position outwardly toward carriers held in the carrier supports.5. A centrifugal cleaner for carriers according to claim 1 and whereinthe rotor extends upwardly from lower portions of the processing chamberwithin a rotor support housing mounted within the processing chamber;said rotor also including a rotor wheel having openings therein alongupper portions thereof; said rotor further including a rotor cage whichis mounted to said rotor wheel and extends downwardly to support saidplurality of carrier supports.
 6. A centrifugal cleaner for carriersaccording to claim 1 and wherein the rotor extends upwardly from lowerportions of the processing chamber within a rotor support housingmounted within the processing chamber; said rotor also including a rotorwheel along upper portions thereof; said rotor further including a rotorcage which is mounted to said rotor wheel and extends downwardly; andwherein said plurality of outer and inner supplies includes a pluralityof cleaning liquid sprayer manifolds; said sprayer manifolds includingouter sprayer manifolds for spraying from outer positions inwardlytoward carriers held in the carrier supports, and inner sprayermanifolds for spraying from inner positions outwardly toward carriersheld in the carrier supports; said inner sprayer manifolds extendingupwardly within the processing chamber between the rotor cage and therotor support housing.
 7. A centrifugal cleaner for carriers accordingto claim 1 and wherein the rotor extends upwardly from lower portions ofthe processing chamber; said rotor further including a rotor cage tosupport said plurality of carrier supports.
 8. A centrifugal cleaner forcarriers according to claim 1 and wherein the rotor includes a rotorshaft which extends upwardly from lower portions of the processingchamber; said rotor further including a rotor cage having downwardlyextending portions; said plurality of outer and inner supplies includesmultiple spray manifolds including at least one inner spray manifoldwhich extends upwardly within the processing chamber between the rotorcage and the rotor shaft, and at least one outer spray manifold which isoutward from the rotor cage.
 9. A centrifugal cleaner for carriersaccording to claim 1 and wherein the rotor includes portions whichinduce air flow through the vessel.
 10. A centrifugal cleaner forcarriers according to claim 1 and wherein the rotor includes a rotorshaft which extends upwardly from lower portions of the processingchamber; said rotor further including a rotor cage having downwardlyextending portions; said plurality of inner supplies being positioned toextend within the rotor cage.
 11. A centrifugal cleaner for carriersaccording to claim 1 and further comprising at least one drying gasfilter for filtering contaminants from drying gas supplied to theprocess chamber through said at least one drying gas supply.
 12. Acentrifugal cleaner for carriers according to claim 1 and furthercomprising:at least one drying gas filter for filtering contaminantsfrom drying gas supplied to the process chamber through said at leastone drying gas supply; at least one drying gas heater for heating dryinggas supplied to the process chamber through said at least one drying gassupply.
 13. A centrifugal cleaner for carriers according to claim 1 andfurther comprising:a drying gas plenum; at least one drying gas filterfor filtering contaminants from drying gas supplied to said drying gasplenum; at least one drying gas heater mounted to the drying gas plenumfor heating filtered drying gas; and wherein filtered, heated drying gasfrom said plenum is supplied to the process chamber.
 14. A centrifugalcleaner for carriers according to claim 1 and wherein at least onedrying gas supply is approximately aligned with the rotational axis ofsaid rotor.
 15. A centrifugal cleaner for carriers according to claim 1wherein said plurality of outer and inner supplies includes a pluralityof spray manifolds; and further comprising a plurality of drying gasmanifolds for jetting drying gas upon the carrier supports and anycarriers held therein to aid in drying cleaning liquid therefrom.
 16. Acentrifugal cleaner for carriers according to claim 1 and wherein saidplurality of outer and inner supplies includes:a plurality of spraymanifolds; said spray manifolds including outer spray manifolds forspraying from outer positions inwardly toward carriers held in thecarrier supports, and inner spray manifolds for spraying from innerpositions outwardly toward carriers held in the carrier supports; and aplurality of drying gas manifolds for jetting drying gas upon thecarrier supports and any carriers held therein to aid in drying cleaningliquid therefrom.
 17. A centrifugal cleaner for carriers according toclaim 1 and further defined by said at least one door being slidable.18. A centrifugal cleaner for carriers according to claim 1 whereinthere are distinct entrance and exit ports, and distinct entrance andexit doors which controllably open and close said ports, respectively.19. A centrifugal cleaner for carriers according to claim 1 whereinthere are distinct entrance and exit ports, and distinct entrance andexit doors which controllably open and close said ports, respectively;said entrance and exit doors being slidable.
 20. A centrifugal cleanerfor cleaning carriers used in semiconductor processing, comprising:aframe; a processing vessel defining a process chamber therewithin; atleast one port to allow passage of carriers relative to the processchamber; at least one door for controllably opening and closing saidport; a rotor mounted for rotation within the process chamber; at leastone carrier support connected to said rotor for holding carriers duringcentrifugal cleaning; rotor drive means for controllably rotating saidrotor; at least one cleaning liquid sprayer mounted within the processchamber for spraying a suitable cleaning liquid upon carriers held inthe carrier supports; at least one primary drying gas supply forsupplying primary drying gas to the process chamber to dry said cleaningliquid from carriers; said at least one primary drying gas supplyincluding at least one port through which drying gas flows from upperportions of the process chamber downwardly; at least one secondarydrying gas supply for jetting secondary drying gas onto carriers held inthe at least one carrier support.
 21. A centrifugal cleaner for carriersaccording to claim 20 and further comprising at least one drying gasfilter for filtering contaminants from drying gas supplied to theprocess chamber through said at least one primary drying gas supply. 22.A centrifugal cleaner for carriers according to claim 20 and furthercomprising:at least one drying gas filter for filtering contaminantsfrom drying gas supplied to the process chamber through said at leastone primary drying gas supply; at least one drying gas heater forheating drying gas supplied to the process chamber through said at leastone primary drying gas supply.
 23. A centrifugal cleaner for carriersaccording to claim 20 and further comprising:a drying gas plenum; atleast one drying gas filter for filtering contaminants from drying gassupplied to said drying gas plenum; at least one drying gas heatermounted to the drying gas plenum for heating filtered drying gas; andwherein filtered, heated drying gas from said plenum is supplied to theprocess chamber through said at least one primary drying gas supply. 24.A centrifugal cleaner for carriers according to claim 20 and whereinsaid at least one primary drying gas supply is approximately alignedwith the rotational axis of said rotor.
 25. A centrifugal cleaner forcarriers according to claim 20 and wherein the rotor extends upwardlyfrom lower portions of the processing chamber.
 26. A centrifugal cleanerfor carriers according to claim 20 and wherein the rotor extendsupwardly from lower portions of the processing chamber within a rotorsupport housing mounted within the processing chamber.
 27. A centrifugalcleaner for carriers according to claim 20 and wherein the rotor extendsupwardly from lower portions of the processing chamber within a rotorsupport housing mounted within the processing chamber; said rotor alsoincluding a rotor wheel having openings therein along upper portionsthereof; said rotor further including a rotor cage which is mounted tosaid rotor wheel and extends downwardly to support said plurality ofcarrier supports.
 28. A centrifugal cleaner for carriers according toclaim 20 and wherein the rotor extends upwardly from lower portions ofthe processing chamber within a rotor support housing mounted within theprocessing chamber; said rotor also including a rotor wheel along upperportions thereof; said rotor further including a rotor cage which ismounted to said rotor wheel and extends downwardly; said at least onecleaning liquid sprayer including at least one inner spray manifoldwhich extends upwardly within the processing chamber between the rotorcage and the rotor support housing.
 29. A centrifugal cleaner forcarriers according to claim 20 and wherein the rotor extends upwardlyfrom lower portions of the processing chamber; said rotor furtherincluding a rotor cage to support said plurality of carrier supports.30. A centrifugal cleaner for carriers according to claim 20 and whereinthe rotor includes a rotor shaft which extends upwardly from lowerportions of the processing chamber; said rotor further including a rotorcage having downwardly extending portions; said at least one cleaningliquid sprayer having multiple spray manifolds including at least oneinner spray manifold which extends upwardly within the processingchamber between the rotor cage and the rotor shaft.
 31. A centrifugalcleaner for carriers according to claim 20 and wherein the rotorincludes a rotor shaft; said rotor further including a rotor cage; saidat least one cleaning liquid sprayer having multiple spray manifoldsincluding at least one inner spray manifold which extends upwardlywithin the processing chamber between the rotor cage and the rotorshaft, and at least one outer spray manifold which is outward from therotor cage.
 32. A centrifugal cleaner for carriers according to claim 20and wherein said at least one cleaning liquid sprayer includes aplurality of spray manifolds; said spray manifolds including outer spraymanifolds for spraying from outer positions inwardly toward carriersheld in the carrier supports, and inner spray manifolds for sprayingfrom inner positions outwardly toward carriers held in the carriersupports.
 33. A centrifugal cleaner for carriers according to claim 20wherein said at least one cleaning liquid sprayer includes a pluralityof spray manifolds; and further comprising a plurality of secondarydrying gas manifolds for jetting drying gas upon the carrier supportsand any carriers held therein to aid in drying cleaning liquidtherefrom.
 34. A centrifugal cleaner for carriers according to claim 20and wherein said at least one cleaning liquid sprayer includes aplurality of spray manifolds; said spray manifolds including outer spraymanifolds for spraying from outer positions inwardly toward carriersheld in the carrier supports, and inner spray manifolds for sprayingfrom inner positions outwardly toward carriers held in the carriersupports; and said at least one secondary drying gas supply furthercomprising a plurality of drying gas manifolds for jetting drying gasupon the carrier supports and any carriers held therein to aid in dryingcleaning liquid therefrom.
 35. A centrifugal cleaner for carriersaccording to claim 20 and further comprising a lower baffle spaced fromand adjacent to a bottom of the process chamber.
 36. A centrifugalcleaner for carriers according to claim 20 and further defined by saidat least one door being slidable.
 37. A centrifugal cleaner for carriersaccording to claim 20 wherein there are distinct entrance and exitports, and distinct entrance and exit doors which controllably open andclose said ports, respectively.
 38. A centrifugal cleaner for carriersaccording to claim 20 wherein there are distinct entrance and exitports, and distinct entrance and exit doors which controllably open andclose said ports, respectively; said entrance and exit doors beingslidable.
 39. A centrifugal cleaner for cleaning carriers used insemiconductor processing, comprising:a frame; a processing vesseldefining a process chamber therewithin; at least one port to allowpassage of carriers relative to the process chamber; a door forcontrollably opening and closing said port; a rotor mounted for rotationwithin the process chamber; at least one carrier support connected tosaid rotor for holding carriers during centrifugal cleaning; rotor drivemeans for controllably rotating said rotor; at least one cleaning liquidsprayer mounted within the process chamber for spraying a suitablecleaning liquid upon carriers held in the carrier supports; at least oneprimary drying gas supply for supplying primary drying gas to theprocess chamber to dry said cleaning liquid from carriers; said rotorbeing arranged within the processing chamber and constructed so as toinduce flow of primary drying gas through the at least one primarydrying gas supply and through the processing chamber when the rotor isrotating.
 40. A centrifugal cleaner for carriers according to claim 39and further comprising at least one drying gas filter for filteringcontaminants from drying gas supplied to the process chamber throughsaid at least one primary drying gas supply.
 41. A centrifugal cleanerfor carriers according to claim 39 and further comprising:at least onedrying gas filter for filtering contaminants from primary drying gassupplied to the process chamber through said at least one primary dryinggas supply; at least one drying gas heater for heating drying gassupplied to the process chamber.
 42. A centrifugal cleaner for carriersaccording to claim 39 and further comprising:a drying gas plenum; atleast one drying gas filter for filtering contaminants from drying gassupplied to said drying gas plenum; at least one drying gas heatermounted to the drying gas plenum for heating filtered drying gas; andwherein filtered, heated drying gas from said plenum is supplied to theprocess chamber through said at least one primary drying gas supply. 43.A centrifugal cleaner for carriers according to claim 39 and whereinsaid at least one primary drying gas supply is approximately alignedwith the rotational axis of said rotor.
 44. A centrifugal cleaner forcarriers according to claim 39 and wherein the rotor extends upwardlyfrom lower portions of the processing chamber.
 45. A centrifugal cleanerfor carriers according to claim 39 and wherein the rotor extendsupwardly from lower portions of the processing chamber within a rotorsupport housing mounted within the processing chamber.
 46. A centrifugalcleaner for carriers according to claim 39 and wherein the rotor extendsupwardly from lower portions of the processing chamber within a rotorsupport housing mounted within the processing chamber; said rotor alsoincluding a rotor wheel having openings thereon along upper portionsthereof; said rotor further including a rotor cage which is mounted tosaid rotor wheel and extends downwardly to support said plurality ofcarrier supports.
 47. A centrifugal cleaner for carriers according toclaim 39 and wherein the rotor extends upwardly from lower portions ofthe processing chamber within a rotor support housing mounted within theprocessing chamber; said rotor also including a rotor wheel havingopenings along upper portions thereof; said rotor further including arotor cage which is mounted to said rotor wheel and extends downwardly;said at least one cleaning liquid sprayer including at least one innerspray manifold which extends upwardly within the processing chamberbetween the rotor cage and the rotor support housing.
 48. A centrifugalcleaner for carriers according to claim 39 and wherein the rotor extendsupwardly from lower portions of the processing chamber; said rotorfurther including a rotor cage to support said plurality of carriersupports.
 49. A centrifugal cleaner for carriers according to claim 39and wherein the rotor includes a rotor shaft which extends upwardly fromlower portions of the processing chamber; said rotor further including arotor cage having downwardly extending portions; said at least onecleaning liquid sprayer having multiple spray manifolds including atleast one inner spray manifold which extends upwardly within theprocessing chamber between the rotor cage and the rotor shaft.
 50. Acentrifugal cleaner for carriers according to claim 39 and wherein therotor includes a rotor shaft; said rotor further including a rotor cage;said at least one cleaning liquid sprayer having multiple spraymanifolds including at least one inner spray manifold which extendsupwardly within the processing chamber between the rotor cage and therotor shaft, and at least one outer spray manifold which is outward fromthe rotor cage.
 51. A centrifugal cleaner for carriers according toclaim 39 and wherein said at least one cleaning liquid sprayer includesa plurality of spray manifolds; said spray manifolds including outerspray manifolds for spraying from outer positions inwardly towardcarriers held in the carrier supports, and inner spray manifolds forspraying from inner positions outwardly toward carriers held in thecarrier supports.
 52. A centrifugal cleaner for carriers according toclaim 39 wherein said at least one cleaning liquid sprayer includes aplurality of spray manifolds; and further comprising a plurality ofsecondary drying gas manifolds for jetting drying gas upon the carriersupports and any carriers held therein to aid in drying cleaning liquidtherefrom.
 53. A centrifugal cleaner for carriers according to claim 39and wherein said at least one cleaning liquid sprayer includes aplurality of spray manifolds; said spray manifolds including outer spraymanifolds for spraying from outer positions inwardly toward carriersheld in the carrier supports, and inner spray manifolds for sprayingfrom inner positions outwardly toward carriers held in the carriersupports; and said at least one secondary drying gas supply furthercomprising a plurality of drying gas manifolds for jetting drying gasupon the carrier supports and any carriers held therein to aid in dryingcleaning liquid therefrom.
 54. A centrifugal cleaner for carriersaccording to claim 39 and further comprising a lower baffle spaced fromand adjacent to a bottom of the process chamber.
 55. A centrifugalcleaner for carriers according to claim 39 and further defined by saidat least one door being slidable.
 56. A centrifugal cleaner for carriersaccording to claim 39 wherein there are distinct entrance and exitports, and distinct entrance and exit doors which controllably open andclose said ports, respectively.
 57. A centrifugal cleaner for carriersaccording to claim 39 wherein there are distinct entrance and exitports, and distinct entrance and exit doors which controllably open andclose said ports, respectively; said entrance and exit doors beingslidable.